chore: no tracked Cargo.lock — compile from the latest resolution

Decision (operator, 2026-10-16): no pins. The lock is removed from the
tree and ignored so every build resolves the git-branch dependencies at
their current heads instead of a frozen graph.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017SNHxJYC1MeW3HsyhGZo1E

Author: claude

.gitignore

@@ -39,3 +39,6 @@ valhalla-lab/reproducers/r8-ndarray/target/
 # interop/tinkerpop: fetched jars and compiled classes (fetch-deps.sh / run.sh)
 /interop/tinkerpop/lib/
 /interop/tinkerpop/out/
+
+# No tracked Cargo.lock (no pins, 2026-10-16): builds resolve the latest heads.
+Cargo.lock